The invention herein relates to a system for treating cooking oils. More particularly it relates to a system for treating cooking oils which are operated at high temperatures for long periods of time.
In recent years there has been a substantial growth in the "fast food" type of restaurants. Many of these restaurants specialize in cooking and serving a limited variety of foods, most of them fried foods such as chicken, potatoes, pies and fish. In addition, most conventional restaurants also offer fried foods such as chicken and potatoes as part of their menus.
In these frying operations large quantities of edible cooking oils are heated in vats to temperatures on the order of approximately 350.degree. F. to 375.degree. F. (175.degree. C. to 190.degree. C.) and the food immersed in the hot oil for cooking. The oil is reused repeatedly for cooking subsequent batches of food and is maintained at these high temperatures for prolonged periods. During this continued operation the high temperature frying reactions cause the formation of free fatty acids (FFA) in the oil. In addition, the oil becomes badly discolored. The presence of the free fatty acids, which are the precursors of soaps, can impart to the food an objectionable taste. An increase in the FFA content also causes decreases in the oil's smoke point, flash point and fire point, all of which result in increasing smoke and fire hazards as the oil ages. The discolored oil can impart objectionable color to the food which, while not harmful in itself, is often interpreted by the consumer as indicating that the food is substandard.
In the past it has been conventional practice for the fast food outlets and restaurants to filter their cooking oils on a regular basis using conventional filter paper and/or filter aids. Some fast food outlets have used continuous filtration systems and others have used batch systems where the cooking oil is filtered completely 1 to 4 times per day. Filter aids such as perlite, diatomite and clay have been sold under various trade names for use in cooking oil filtration. These filter aids, however, serve only to remove solid particulate matter such as pieces of food or breading from the oils; they do not affect the concentration of FFA nor (with the exception of the bleaching clays) do they affect the color darkening of the oil. Synthetic calcium and/or magnesium silicate hydrates have been used in the past for treating of dry cleaners' solvents (see, e.g., U.S. Pat. Nos. 3,099,626 and 3,427,249). While these materials do serve as FFA adsorbents and/or color control agents, their normal physical structure is such that filtrate flow rate through them is exceedingly slow and therefore they are not satisfactory for use in restaurants and fast food outlets where large quantities of cooking oil must be filtered rapidly (see FIG. 3).
It has been found in practice that cooking oils used in the normal course of business of restaurants and fast food outlets, even if filtered regularly, become unusable within approximately 5 to 10 days because of the buildup of FFA and the excessive discoloration. It is thus evident that it would be of real advantage to have a treating agent which would function as both a filter aid and a high flow rate treating agent which would control the FFA buildup and reduce discoloration, thus prolonging the service life of cooking oil.